And that wasn't the point. The question is whether AIOs are gaining in popularity (as reflected in market share) vs towers.
Evidently Dell believes there is a market, likely a growing one, that they wish to address by adding an AIO to their product line.
The certainly wouldn't do so for something that is of very marginal potential.
How's that treating them? I know you like to pass Sony off as a "premium" PC maker, but when it came to desktops they were making the same low end MicroATX crap as HP, Gateway, and Dell. They just charged more for it. Sony is a laptop maker with some moves into home entertainment center computer. That' their niche. They operate in something called any open market where different companies are Able to fill different requirements.
Probably pretty good. AIOs have better margins than their desktop counterparts and better Average Sale Prices (ASPs).
For a tower you simply can't sell at a premium and Sony, with their VAIO line offered lifestyle integration software (typically tied to other sony products) in much the same way Apple does with iLife. Many VAIOs came with TV tuners and a media bent different from the HPs and Dells of the period. So yes, they were premium machines with Sony styling (something you like, or not).
Note that Toshiba had withdrawn from the desktop market long ago as well. It is #5 worldwide and in the US. Apple has NEVER needed to cater to the tower market to do well given Toshiba has consistently been ahead of it. If Apple did nothing but laptops and Mac Pros it probably would still see growth...although they'd likely have to change up their laptop line a bit.
So AIOs are prefectly viable desktops that are gaining in popularity to the point where Apple has some competition in that market space where before it was largely alone.